System for recycling spent sulfuric acid, method for recycling spent sulfuric waste liquid, and recycled sulfuric acid

ABSTRACT

A system for recycling spent sulfuric acid, wherein spent sulfuric acid is effectively utilized at a place other than a discharge source regardless of geographical conditions, and a method for recycling waste sulfuric acid. In the system, when spent sulfuric acid that is discharged or collected at a discharge source is transported by a carrier unit and used at a user office a concentration of the spent sulfuric acid is measured and/or adjusted at least at one of the discharge source, the carrier unit, and the user office. The spent sulfuric acid waste liquid that is discharged or collected at the discharge source is reutilized by being mixed with at least one of a hydrogen peroxide solution and water.

TECHNICAL FIELD

The present invention relates to a system for recycling spent sulfuricacid, to recycled spent sulfuric acid, to a method for recycling spentsulfuric acid, and to recycled sulfuric acid.

BACKGROUND ART

Sulfuric acid is utilized in large quantity in various kinds ofindustries with a grade (at a purity or a concentration) determinedaccording to purposes of the industries. In the case that such sulfuricacids are spent, various methods for recycling the sulfuric acids havebeen proposed (in Japanese Patent Application Publication Laid-Open Nos.9-315806, and 2002-68715, and so on), and, currently, the followingprocesses are commonly performed.

(1) Wastewater treatment (or neutralization treatment) is performedthereon in a generating plant.

(2) A specialized processor picks up (or collects) spent sulfuric acidsand performs wastewater treatment thereon.

(3) Spent sulfuric acids are utilized in a plant as a neutralizer.

(4) Sulfuric waste liquid is recycled (or subjected to distillationpurification) in a plant or by a specialized recycler.

(5) Spent sulfuric acid is taken over to a specialized recycler, andutilized as a material of alum (or aluminium sulfate) (incidentally, inthis case, the usage rate of spent sulfuric acid is equal to or lessthan 10%).

(6) Spent sulfuric acid is collected by a specialized recycler, and isresold to other users by mixing with virgin sulfuric acid.

In the above case (1), sulfuric acid itself is a strongly acidicpowerful drug and therefore cannot be discarded as it is, andneutralization treatment by using a large amount of neutralizer, such asalkali (for example, slaked lime or the like), orcoagulation-sedimentation treatment or hydrogen peroxide removaltreatment by using various wastewater treatment agents (for instance,inorganic coagulant, polymer coagulant, or hydrogen peroxidedecomposition accelerator) is required, and resultantly a large amountof sludge and wastewater are to be generated. Regarding the above case(2), it is the same with the case (1), except that the treatment isperformed on the spent sulfuric acids outside a plant. In the above case(3), a demand for using the spent sulfuric acid as the neutralizer issmall, and consequently, the same treatment as required in the case (1)is needed for treating a surplus part of the spent sulfuric. In the case(4), a huge plant and energy are needed for recycling the spent sulfuricacid, and the recycling thereof is largely affected by the location (orsite condition) of the plant, so that a target area therefor is limitedonly to a partial restricted area. Moreover, the provision of recyclingequipment in a generating plant is fraught with many problems in energy,cost, site area, safety, and handling thereof and thus impractical andhardly in common use. In the above case (5), waste sulfuric acid isseldom treated as a valuable resource, and usually, the waste sulfuricacid is taken over at charge or sold at a low price (several yen perkilograms). The waste sulfuric acid is transported by way of a path froma discharge source to a user through a specialized recycler, so that atransportation distance is elongated, and similarly with the above case(4), the utilization is largely affected by the location (or sitecondition). Similarly, in the above case (6), the spent sulfuric acid istransported by way of a path from a discharge source to a user through aspecialized recycler. Thus, the transportation distance is elongated andthe mixture is susceptible to the location (or site condition).

As described above, according to the prior art, the recycling of spentsulfuric acid is susceptible to the location of a specialized recyclerthat practices collection/takeover of spent sulfuric acid. Therefore,generally, in a case where no specialized recyclers are present in thevicinity of an own plant, wastewater treatment is performed in the ownplant, and the recycling of spent sulfuric acid has not fully beenestablished. According to the prior art, an added-value of spentsulfuric acid is low, and accordingly, wastewater treatment is usuallyperformed by the above process (1) or (2) in general. Alternatively, thespent sulfuric acid is treated by being delivered to outsiders forvalue. However, it is obvious from the viewpoint of environmentprotection countermeasures that environmental destruction isincreasingly promoted by repeating a treatment process, which is seen inthe above case (1) or (2) and uses a large amount of chemicals tothereby generate large amounts of sludge and wastewater.

Thus, there has been an increasing demand for developing techniquesrelated to a method of recycling spent sulfuric acid, and each officeadvances development directed to simplification and energy-saving of themethod and equipment for performing the method. For example, a method ofintroducing sulfurous acid to spent sulfuric acid thereby to decompose aresidual hydrogen peroxide solution and to generate sulfuric acid (seeJapanese Patent Application Publication Laid-Open No. 9-135806) and amethod of supplying spent sulfuric acid to an electrolytic cellconstituted by anion-exchange membrane and cation-exchange membranethereby to concentrate sulfuric acid and to generate oxidant (seeJapanese Patent Application Publication Laid-Open No. 5-139707) havebeen studied in each office that undertakes various efforts directed toscaling-down of a plant and to energy-saving. However, these techniqueshave faced many problems in cost and so on. Thus, it cannot be said thata practical method of recycling spent sulfuric acid has fully beenestablished.

An object of the invention is to provide an industrially advantageousnew system featuring that spent sulfuric acid is effectively utilized ata place other than a discharge source regardless of geographicalconditions.

Further, another object of the invention is to provide a system which isable to recycle spent sulfuric acid, without being equipped with alarge-scale facility, at low cost by supplying the spent sulfuric acidto an appropriate user according to the necessary purity and amountthereof and by recycling the supplied acid.

Furthermore, further another object of the invention is to provide anindustrially advantageous recycling method featuring that sulfuric wasteliquid discharged from a certain office is effectively utilized bymixing the waste liquid with at least one of a hydrogen peroxidesolution and water to thereby add a value to the sulfuric waste liquid,and to provide value-added recycled sulfuric acid.

Moreover, still another object of the invention is to provide a methodenabled to recycle spent sulfuric acid at low cost without setting up alarge-scale facility.

DISCLOSURE OF THE INVENTION

As a result of conducting diligent studies to achieve the foregoingobjects, the present inventors have found that for the purpose ofeffectively utilizing spent sulfuric acid, which is discharged/collectedat a certain office, at another office, by measuring and adjusting aconcentration of the spent sulfuric acid at least at one of a spentsulfuric acid generating office, a spent sulfuric acid transporter, anda spent sulfuric acid utilizing office, it becomes possible toeffectively utilize the spent sulfuric acid with having little effect ofa location. The inventors have accomplished the invention by conductingvarious additional studies.

Further, the inventors have found that for the purpose of effectivelyutilizing spent sulfuric acid, which is discharged and/or collected at acertain office, the spent sulfuric acid can be utilized as recycledsulfuric acid by mixing at least one of a hydrogen peroxide solution andwater into the spent sulfuric acid. The inventors have completed theinvention by conducting various additional studies.

BRIEF DESCRIPTION of DRAWINGS

FIGS. 1A and 1B are views each illustrating a flow of conventionaltreatment of spent sulfuric acid waste liquid.

FIG. 2 is a view illustrating a mode in a conventional method of reusingspent sulfuric acid by refinement and recovery.

FIG. 3 is a view illustrating a flow of conventional treatment of spentsulfuric acid.

FIGS. 4A to 4C are views each illustrating a mode of a system forrecycling spent sulfuric acid according to the invention.

FIG. 5 is a view illustrating other modes of the system for recyclingspent sulfuric acid according to the invention.

FIG. 6 is a view illustrating a more practical mode of the system forrecycling spent sulfuric acid according to the invention.

FIG. 7 is a view illustrating a mode of a method of recycling spentsulfuric acid according to the invention.

FIGS. 8A to 8C are views respectively illustrating other modes of themethod of recycling spent sulfuric acid according to the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

There is no particular limitation on the concentration of spent sulfuricacid to be treated according to the invention, however, spent sulfuricacid of higher concentration is more preferable for cutting down thetransportation cost per unit weight of pure sulfuric acid to a low levelin order to improve the practicality of the invention, because thehigher the concentration of spent sulfuric acid is, the higher theefficiency in transporting the spent sulfuric acid becomes. Further,sulfuric acid waste liquid, in which a hydrogen peroxide solution ismixed, is more preferable. It is because the facts that hydrogenperoxide used for sterilizing and deodorizing medical instruments is astrong oxidizing agent, and that a mixture solution obtained by mixing ahydrogen peroxide solution into sulfuric acid, which is oxidizing strongacid, has a very strong oxidizing force and can oxidize, dissolve, andeliminate organic and inorganic materials, and also can be expected tobe used as various kinds of cleaning liquid. From the above-mentionedviewpoints, sulfuric acid waste liquid discharged from a semiconductoroffice is preferable as the sulfuric waste liquid suitable for thepresent invention for the following reason. That is, the semiconductoroffice utilizes a mixture solution obtained by mixing strong sulfuricacid, which has a low content of impurities, with a hydrogen peroxidesolution as a cleaning solution in a semiconductor manufacturingprocess. Thus, sulfuric acid waste liquid, which is high inconcentration and purity and contains a hydrogen peroxide solution, canbe obtained by collecting spent sulfuric acid waste liquid withoutchange.

As above-mentioned, sulfuric acid waste liquid mixed with hydrogenperoxide, which is generated in the semiconductor office, is usuallywastewater-treated or utilized as a neutralizing agent in a plant.Sometimes, sulfuric acid waste liquid mixed with a hydrogen peroxidesolution is utilized outside the plant as a material of alum. However,the hydrogen peroxide solution mixed therein is not effectivelyutilized. This is merely cascade utilization of the sulfuric acid wasteliquid mixed with hydrogen peroxide (simply as an alternative ofindustrial sulfuric acid), because it is a demerit that a hydrogenperoxide solution is mixed into the sulfuric acid waste liquid tothereby considerably lower the added-value of the sulfuric acid wasteliquid.

According to the invention, the addition of hydrogen peroxide solutionand/or water to the sulfuric acid waste liquid is performed so that thehydrogen peroxide solution has a predetermined concentration. Thus,hydrogen peroxide already contained in the waste liquid causes notrouble. On the contrary, the invention is advantageous in that aquantity of hydrogen peroxide solution to be added is reduced by anamount of residual hydrogen peroxide solution in the waste liquid.

Sulfuric acid waste liquid having a high concentration, which isdischarged from the semiconductor office, is preferable, because thehigher the concentration thereof, that is, the lower the content ofimpurity is, the larger an amount of reusable matter becomes, butusually, a sulfuric acid content ranges from 50 weight percent to 98weight percent. More generally, the sulfuric acid content ranges from 65weight percent to 90 weight percent. Further, the content of hydrogenperoxide contained in the sulfuric acid waste liquid ranges from 0 to 6weight percent. More generally, the content thereof ranges from 0.1weight percent to 3 weight percent. Further, demands for purity ofsulfuric acid for electronic industry have become stringent along withminiaturization and high densification of semiconductor devices. It isdemanded that the content of, for example, metal ingredients is equal toor less than 20 ppb. Therefore, preferably, the level of the purity ofsulfuric acid is so high that the contents of various kinds ofimpurities contained in the sulfuric acid waste liquid, for instance,the content of metal ingredient is less than 10 ppb, and the content ofchloride is less than 0.1 ppm. This enables that the sulfuric acid wasteliquid is used as cleaning liquid in an office other than thesemiconductor office. For example, the sulfuric acid waste liquid can beused as photoresist mask peeling liquid in a cathode-ray tubemanufacturing office, and as copper-foil etching liquid in acircuit-board manufacturing office. In each of theses cases, an aqueousmixture solution of low-concentration sulfuric acid (having aconcentration ranging from a few tenths weight percent to 40 weightpercent) and a low-concentration hydrogen peroxide solution (having aconcentration ranging from several hundredths weight percent to 40weight percent). Therefore, it is more preferable to utilize thesulfuric acid waste liquid mixed with hydrogen peroxide, which isdischarged from the semiconductor office, for these uses.

An office A discharging sulfuric acid waste liquid according to theinvention is not particularly limited, as long as the office Adischarges sulfuric acid waste liquid having a high sulfuric acidcontent and a low impurity content. Such offices A are, for example,plants or offices in various industries, such as electric/electronicindustries, which include a semiconductor industry, iron and steelindustries, an inorganic drug industry, an organic drug industry, amedicine industry, a textile industry, a fertilizer industry, a metalindustry, a mining industry, a paper manufacturing industry, a sodaindustry, a machine industry, a storage battery industry, and aneutralizing gypsum industry. Among these industries, semiconductor,drug, medicine, and chemical industries are preferable. Especially,judging from the facts that the content of impurities, such as heavymetals, in spent sulfuric acid waste liquid discharged from asemiconductor office is low (at levels of the order of ppm to ppt), andthat a sulfuric acid content thereof is equal to or more than 60 weightpercent, and from the quality, purity, and safety of sulfuric acid wasteliquid, preferably, the office A is a semiconductor office or a plant.

An office C utilizing sulfuric acid waste liquid, which is to beincluded in the invention, is not particularly limited. Such offices Care, for example, plants or offices in various industries, such aselectric/electronic industries (including a cathode-ray tube office anda circuit-board office), and iron and steel industries, an inorganicdrug industry, an organic drug industry, a medicine industry, a textileindustry, a fertilizer industry, a metal industry, a mining industry, apaper manufacturing industry, a soda industry, a machine industry, astorage battery industry, and a neutralizing gypsum industry. Among theplants or the offices in these industries, the plants or the offices inthe electric/electronic industries (including a cathode-ray tube officeand a circuit-board office), the chemical industry, the machineindustry, or the iron and steel industries. Especially, plants oroffices in the electric/electronic industries including a cathode-raytube office and a circuit-board office), are preferable. Practicalexamples of these are a cathode-ray tube office and a circuit-boardoffice. At these offices, a dilute mixture aqueous solution of sulfuricacid and hydrogen peroxide solution is utilized as the photoresist maskpeeling liquid and as copper-foil peeling liquid. The concentration ofsulfuric acid contained in the mixture solution is usually equal to orless than 50 weight percent. This is preferable for reutilizing spentsulfuric acid discharged from the office A.

A carrier unit B moving sulfuric acid waste liquid, which is to beincluded in the invention, is not particularly limited. Such carrierunits B are, for example, vehicles (for instance, a tank truck, and atruck), ships (for example, a tanker, and a ferry), freight trains,airplanes (or an air freighter). Among these units, the vehicles and theships are more practical. Especially, the tank truck and the truck (amedicine container that transports medicine) easily make access to theuser office C from the discharge source office A. Thus, the applicableranges of the tank truck and the truck are wider than othertransportation means.

The spent-sulfuric-acid recycling system according to the inventionfeatures that the concentration of spent sulfuric acid is measuredand/or adjusted at least at one of the discharge source A, the carrierunit B, and the user office C. Especially, it is preferable that theconcentration of spent sulfuric acid is adjusted according to a resultof measuring the concentration of the spent sulfuric acid.

Means for measuring the concentration of spent sulfuric acid, which isto be included in the invention, is not particularly limited, and may beincluded the following means. That is, at least one kind of means formeasuring a refractive index, means for performing neutralizationtitration, means for measuring moisture content (according to a KarlFischer's method, or what is called an evaporated residue method), meansfor measuring absorbance, means for measuring specific gravity, meansfor measuring viscosity, means for measuring pH, and means forperforming potentiometric titration is used, so that the concentrationof spent sulfuric acid can be measured. Among these means, from theviewpoints of measurement speed and accuracy, and the price and size ofa measuring instrument, and handling ability, the means for measuring arefractive index, the means for measuring specific gravity, and themeans for measuring pH are more preferable. The above-mentionedconcentration measurement may be performed at any one of the dischargesource A, from which spent sulfuric acid is discharged, the carrier unitB transporting the spent sulfuric acid, and the user office C utilizingthe spent sulfuric acid, alternatively, at two or more of the dischargesource, the carrier unit, and the user office. A reference value forconcentration adjustment (to be described later) is obtained byperforming the concentration measurement in this way. Further, even whenconcentration adjustment is not performed, the presentation of a resultof the concentration measurement to the user office C leads to assuranceof the quality of recycled sulfuric acid. Furthermore, the price ofspent sulfuric acid can be determined according to a result of themeasurement of the concentration of the spent sulfuric acid.

The concentration adjustment to be included in the invention may beperformed in either of the cases that the concentration of the spentsulfuric acid is increased, and that the concentration thereof isdecreased. However, it is more general that the concentration thereof isadjusted by being decreased to a lower value. To increase theconcentration thereof, sulfuric anhydride or fuming sulfuric acid isadded thereto. Further, the adjustment of the concentration thereof to alower value is enabled by adding water or purified water thereto.Incidentally, methods of adjusting the concentration of spent sulfuricacid to a predetermined value are a method of adding a constant amount(per volume or per weight) of concentration adjustment liquid (sulfuricanhydride, fuming sulfuric acid, water, purified water, and so forth) tospent sulfuric acid, and a method of adding a predetermined amount ofconcentration adjustment liquid thereto according to a result of theconcentration measurement. From the viewpoint of quality control, thelatter method is more preferable. The above-mentioned concentrationadjustment may be performed at any one of the discharge source A, thecarrier unit B, and the user office C, alternatively, at two or more ofthe discharge source, the carrier unit, and the user office.

The concentration measurement and the concentration adjustment may beperformed either at the same place or at different places. In the casethat the concentration measurement and the concentration adjustment areperformed at the same place, a result of the concentration measurementis directly sent to a concentration adjustment apparatus (concentrationadjustment liquid, a concentration adjustment liquid storing tank, anadjustment liquid supply pump, a blending tank, a concentrationmeasuring apparatus provided in the blending tank and so forth) in theform of a signal. Thus, the concentration can automatically be adjustedto a predetermined value. On the other hand, in the case that theconcentration measurement and the concentration adjustment are performedat different places, a result of the concentration adjustment can betransmitted to the next step by various means, such as orality,telephones, mails, and the Internet. It is judged at a place, to whichthe result of the measurement is transmitted, according to thetransmitted result whether spent sulfuric acid is used without change,or the concentration adjustment is performed. When the concentrationadjustment is performed, the concentration adjustment liquid is added insuch a way as to obtain a desired concentration, as above-mentioned.Incidentally, in the concentration adjustment tank, the concentrationmeasuring apparatus may be installed so as to check whether theconcentration of the spent sulfuric acid reaches a predetermined valueafter the concentration adjustment liquid is added thereto.

According to the invention, an additional treatment other than themeasurement and/or the adjustment of the concentration of the spentsulfuric acid may be performed at least at one of the discharge sourceA, the carrier unit B, and the user office C. The additional treatment,which will be described in detail below, is, for instance, a treatmentof concentrating sulfuric acid contained in the spent sulfuric acid, atreatment of removing ingredients other than sulfuric acid, which arecontained in the spent sulfuric acid, or a treatment of adding anotheringredient other than the sulfuric acid, which is contained in the spentsulfuric acid, thereto.

The treatment of concentrating sulfuric acid contained in the spentsulfuric acid has been cited as exemplifying the additional treatment.Known means may be used for performing the treatment of concentratingsulfuric acid. For example, in the case where the ingredients, which areother than sulfuric acid and contained in the spent sulfuric acid, arematerials, such as water and hydrogen peroxide solution, which are lowerin boiling point than sulfuric acid, the ingredients are evaporatedfaster than sulfuric acid by heating the spent sulfuric acid.Consequently, the sulfuric acid contained in the spent sulfuric acid canbe concentrated. At that time, the evaporated ingredients are removedfrom a reaction system by using a suction unit. Thus, sulfuric acid canquickly be concentrated, as compared with a case that the gaseousingredient is discharged by natural diffusion. A heating temperature, towhich the spent sulfuric acid is heated in such a treatment, depends onthe ingredients contained in the spent sulfuric acid, which are otherthan sulfuric acid. Therefore, although the heating temperature cannotgenerally be determined, for example, in the case where the spentsulfuric acid contains water and hydrogen peroxide solution, the heatingtemperature ranges from about 150° C. to about 315° C., preferably,about 180° C. to about 250° C. A reaction apparatus used for thetreatment is not particularly limited. A known apparatus may be used asthe reaction apparatus. This apparatus is, for instance, an apparatusthat is made of a material showing corrosion-resistance against spentsulfuric acid under concentrating conditions, and enabled to temporarilystore the spent sulfuric acid, and that has a supply port from which thespent sulfuric acid is supplied, a discharge portion from whichconcentrated solution is taken out, a heating device for heating spentsulfuric acid, an exhaust port from which the gaseous ingredientobtained by evaporation is exhausted, and a suction unit connected tothe exhaust port as an option. More specifically, an example of anapparatus for concentrating sulfuric acid contained in the spentsulfuric acid, in which the sulfuric acid is mixed with hydrogenperoxide solution, is an apparatus described in Japanese PatentApplication Publication Laid-Open No. 2002-68715.

Further, the treatment of removing ingredients other than sulfuric acidcontained in the spent sulfuric acid has been cited as exemplifying theadditional treatment. Specifically, spent sulfuric acid discharged inthe technical field of metal plating frequently contains metal ions.Thus, a treatment of eliminating such metal ions can be cited asexemplifying the treatment of removing ingredients other than sulfuricacid. A treatment of using anion-exchange membrane and separating metalions from a solution, which contains acid and metal, by utilizing aconcentration difference therebetween as a driving force to thereby thatis, what is called diffusion dialysis is cited as exemplifying thetreatment of eliminating the metal ions. Many documents and patentsconcerning membrane for performing diffusion dialysis on acid arereported. Anion-exchange membrane obtained by amination of (orintroduction of quaternary-pyridinium groups to) chlormethyl-styrene (orvinyl pyridine)-divinylbenzene copolymer is the most practical anduseful.

Treatments of removing only hydrogen peroxide solution from spentsulfuric acid containing the hydrogen peroxide solution are cited asexemplifying the treatment of removing ingredients other than sulfuricacid contained in the spent sulfuric acid. More specifically, atreatment of decomposing hydrogen peroxide by simultaneously supplyinghydrogen to a hydrogen peroxide decomposing catalyst (see JapanesePatent Application Publication Laid-Open No. 61-186208), and a treatmentof decomposing hydrogen peroxide by letting waste liquid, whosetemperature is raised, through a carbonaceous material (see JapanesePatent Application Publication Laid-Open No. 5-345188) are cited.Moreover, a treatment of introducing sulfurous acid into spent sulfuricacid, which contains hydrogen peroxide solution, and causing thehydrogen peroxide and the sulfurous acid to react with each otherthereby to decompose hydrogen peroxide and to produce sulfuric acid, andpreventing sulfurous acid by detecting the sulfurous acid fromexcessively being added thereto, and then eliminating residual sulfurousacid by aerating the spent sulfuric acid after the introduction of thesulfurous acid is stopped (see Japanese Patent Application PublicationLaid-Open No. 9-315806).

An additional ingredient other than sulfuric acid may be added to thespent sulfuric acid according to a purpose for using at a user office C.The additional ingredient is not particularly limited. Hydrogen peroxidesolution is cited as exemplifying the additional ingredient, becausesulfuric acid containing hydrogen peroxide solution is frequently usedas an etching agent, and as a surface treatment agent, and so on, formanufacturing a semiconductor, and a printed circuit board, and forperforming surface treatment on various metals.

The added value of spent sulfuric acid, which has hitherto been noteffectively utilized, or which has been sold at low price, can bedramatically increased (as that of a valuable resource) by using theabove-mentioned method. There are three modes of selling spent sulfuricacid are a case that a result of measuring the concentration istransmitted to a purchaser without changing the spent sulfuric acid, acase that the spent sulfuric acid, to which concentration adjustmentliquid is added (incidentally, the concentration thereof is indefiniteafter the concentration adjustment liquid is added), is sold, and a casethat the spent sulfuric acid, to which concentration adjustment liquidis added, is sold by adjusting the concentration thereof to apredetermined value (incidentally, the value of the concentration ischecked). When the spent sulfuric acid is soled, volume (or capacity) orweight thereof may be employed as a basis for sales. Alternatively, thespent sulfuric acid may be sold according to a result of theconcentration measurement by using the content of pure sulfuric acid asthe basis for sales. When the spent sulfuric acid is sold as it is, thatis, without performing the concentration adjustment, the concentrationof the spent sulfuric acid varies at the discharge source. Therefore, itis more rational (or quantitative) to sell the spent sulfuric acid onthe basis of the pure sulfuric acid content.

A system for recycling spent sulfuric acid according to the inventioncan repeat the treatment a plurality of times. That is, sulfuric acidrecycled by the system for recycling spent sulfuric acid according tothe invention may be provided thereto again. More specifically,circulation of the recycling, which is represented by the nextexpression: Discharge Source A→Carrier unit B→User Office C (=DischargeSource A′→Carrier unit B′→User Office C′)n (in the expression, “n”designates a natural number, preferably, a natural number ranging from 1to 7, and incidentally, in the case that “n” is equal to or larger than2, A′, B′, and C′, which correspond to a different value of “n”, may beeither the same as or differ from A, B, and C, respectively.

The system for recycling spent sulfuric acid according to the inventionmay have the following mode. That is, the system cited herein has aterminal of the discharge source A, a terminal of the user office C, anda spent sulfuric acid information management unit connected to theterminals through a network. The system comprises (a) means forinputting information on spent sulfuric acid, (b) means for storing theinformation on the spent sulfuric acid, (c) means for inputtingconditions concerning spent sulfuric acid to be supplied, (d) means forretrieving information, which meets at least part of the conditionsinputted by means (c), from the information stored in the means (b), and(e) means for transmitting the information, which is obtained as aresult of retrieval performed by the means (d), to the terminal of thedischarge source A, to which the information is presented, and/or to theterminal of the user office, from which retrieval conditions areinputted.

The spent sulfuric acid information management unit connected to theterminal of the discharge source A and to the terminal of the useroffice C through the network. The spent sulfuric acid informationmanagement unit has (a) means for receiving information on spentsulfuric acid, which is transmitted from the terminal of the dischargesource A, (b) means for storing the information on the spent sulfuricacid, (c) means for receiving conditions, which are transmitted from theterminal of the user office C and concern spent sulfuric acid that theuser office C wishes to be supplied with, (d) means for retrievinginformation, which meets at least part of the conditions inputted bymeans (c), from the information stored in the means (b), and (e) meansfor transmitting the information, which is obtained as a result ofretrieval performed by the means (d), to the terminal of the dischargesource A, to which the information is presented, and/or to the terminalof the user office, from which retrieval conditions are inputted.

The network may be constituted by either a wireless system or a wiredsystem. For example, the Internet, a network constituted by a LAN, and anetwork connected thereto through leased lines.

The information on spent sulfuric acid, which is transmitted from theterminal of the discharge source A, is not particularly limited, but theinformation concerns, for example, an amount of spent sulfuric aciddischarged, the presence/absence of measurement of the concentration ofspent sulfuric acid, a result of measurement when concentrationmeasurement is performed, the possibility of concentration adjustment ofspent sulfuric acid, (for instance, a kind or a content of) theadditional ingredient contained in spent sulfuric acid, or a deliveryprice.

The system according to the invention may have authentication means forauthenticating a discharge source A when information on sent sulfuricacid is inputted from the terminal of the discharge source A. Further,items, such as a name and an address, which are little changed, andinformation concerning spent sulfuric acid, which has ever beeninputted, may automatically be displayed according to user informationpreliminarily registered corresponding to a login ID and a password.

The conditions, which are transmitted from the terminal of the useroffice C and concern spent sulfuric acid that the user office C wishesto be supplied with, are not particularly limited. The conditions are,for example, an amount of spent sulfuric acid to be supplied, thenecessity for performing measurement of the concentration of spentsulfuric acid, a desired concentration, the necessity for performingconcentration adjustment on spent sulfuric acid, (for instance, a kindor a content of) the additional ingredient contained in spent sulfuricacid, or a desired purchase price.

The system according to the invention may have authentication means forauthenticating the user office C when the conditions, which are inputtedfrom the terminal of the user office C and concern spent sulfuric acidthat the user office C wishes to be supplied with. Further, items, suchas a name and an address, which are little changed, and informationconcerning spent sulfuric acid, which has ever been inputted, mayautomatically be displayed according to user information preliminarilyregistered corresponding to a login ID and a password.

Means for retrieving information in the system according to theinvention may retrieve not only information, which meets all theconditions received by the means (c), but information, which meets atleast part of the conditions inputted by the means (c), from theinformation stored in the means (b). Then, the retrieved information istransmitted to the terminal of the user office C from which theconditions are inputted. At that time, information concerning (forinstance, the address and the name of) the discharge source A, to whichthe retrieved information is presented, may be transmitted thereto.Furthermore, information concerning (for example, the address and thename of) the user office C or/and the conditions, which are transmittedfrom the terminal of the user office C and concern spent sulfuric acidthat the user office C wishes to be supplied with, may be transmitted tothe discharge source A, to which the retrieved information is presented.

Preferably, the system according to the invention further comprises (f)means for storing information on the carrier unit B, and (g) means forselecting the carrier unit B according to at least one conditionselected from locations of the discharge source A and the user office C,an amount of spent sulfuric acid to be transported, and the necessityfor measurement and adjustment of the concentration of spent sulfuricacid. When the carrier unit B is selected, a condition other than theconditions, for example, the transportation cost, the structure and thecharacteristics of the material of the carrier unit B may be added.Incidentally, the “information on the carrier unit B” is notparticularly limited. The “information on the carrier unit B” is, forexample, a control station for the carrier unit B, an amount of spentsulfuric acid, which can be transported at a time, whether or not afacility for concentration measurement or concentration adjustment thecarrier unit B has, and whether or not the carrier unit B has a specialstructure and a special material, and the properties of the specialstructure and the special material when the carrier unit B has a specialstructure or a special material.

Further, in the system according to the invention, more preferably, thespent sulfuric acid information management unit is connected toterminals of managers of the carrier units B through the network and has(h) means for transmitting information on transportation of spentsulfuric acid to the terminal of the manager of the selected carrierunit B. Information on the name and the address of each of the dischargesource A and the user office C, an amount of spent sulfuric acid to betransported, the necessity for concentration measurement andconcentration adjustment of spent sulfuric acid, transportation cost,transportation date and time, and properties of the structure and thematerial of the carrier unit B are cited as exemplifying the“information on transportation of spent sulfuric acid”. Further, the“manager of the carrier unit B” is not particularly limited. Any personmay be employed as the manager, as long as he manages the carrier unitB. Usually, an owner of the carrier unit B is cited as the “manager ofthe carrier unit B”, though the “manager of the carrier unit B” is notlimited to him.

The invention provides a computer-readable recording medium forrecording a program for causing a computer to perform (a) the functionof receiving information on spent sulfuric acid, which is transmittedfrom the terminal of the discharge source A, (b) the function of storingthe information on the spent sulfuric acid, (c) the function ofreceiving conditions, which are transmitted from the terminal of theuser office C and concern spent sulfuric acid that the user office Cwishes to be supplied with, (d) the function of retrieving information,which meets at least part of the conditions inputted by performing thefunction (c), from the information stored by performing the function(b), and (e) the function of transmitting the information, which isobtained as a result of retrieval performed by performing the function(d), to the terminal of the discharge source A, to which the informationis presented, and/or to the terminal of the user office, from whichretrieval conditions are inputted.

Preferably, the recording medium according to the invention furtherrecords thereon a program for causing the computer to perform (h) thefunction of transmitting information on transportation of spent sulfuricacid to the terminal of the manager of the selected carrier unit B.

The program can be provided to users by preliminarily being installedinto a hard disk and a semiconductor memory, which serve as a recordingmedium incorporated into the spent-sulfuric-acid information managementunit according to the invention.

Furthermore, the program can tentatively or permanently be stored inrecording media, such as a floppy (a registered trade mark) disk, aCD-ROM (Compact Disk-Read Only Memory), an MO (Magneto Optical) disk, aDVD (Digital Versatile Disc), a magnetic disk, and a semiconductormemory, and also can be provided as package software.

Furthermore, the program can be transferred to the spent sulfuric acidinformation management unit according to the invention from adownloading site by wireless through a satellite. Alternatively, theprogram is transferred by wire or wireless through a network, such as alocal area network, and the Internet, to the spent sulfuric acidinformation management unit according to the invention, wherein theprogram is stored in an incorporated hard disk.

A recording medium referred to in the present specification is a broadconcept including all of these media. Further, in the presentspecification, the functions describing the program provided in arecording medium may be performed chronologically in the order ofdescription thereof, or may be performed in parallel or individuallyeven when not performed chronologically.

In accordance with a method for recycling spent sulfuric acid accordingto the invention, at least at one of the discharge source office A, thecarrier unit B, and the user office C, measurement of concentration ofspent sulfuric acid and/or concentration adjustment of the spentsulfuric acid is performed by being mixed with at least one of hydrogenperoxide solution and water. Further, preferably, the concentrationadjustment is performed according to a result of measurement of theconcentration of spent sulfuric acid waste liquid, and the concentrationof the sulfuric acid waste liquid is measured after the concentrationadjustment is performed.

Means for measuring the concentration of sulfuric acid waste liquid orof sulfuric acid waste liquid mixed with at least one of hydrogenperoxide solution and water to thereby perform concentration adjustmentis not particularly performed. However, the following means are cited.That is, at least one kind of means for measuring a refractive index,means for performing neutralization titration, means for measuringmoisture content (according to a Karl Fischer's method, or what iscalled an evaporated residue method), means for measuring ultrasonicwaves, means for measuring absorbance, means for measuring specificgravity (or density), means for measuring viscosity, means for measuringpH, and means for performing potentiometric titration is used, so thatthe concentration of spent sulfuric acid can be measured. Among thesemeans, from the viewpoint of measurement speed and accuracy, and theprice and size of a measuring instrument, and handling ability, themeans for measuring a refractive index, the means for measuring specificgravity, the means for measuring pH, the means for measuring ultrasonicwaves, and the means for measuring absorbance are more preferable. Theabove-mentioned concentration measurement may be performed at any one ofthe discharge source A, from which spent sulfuric acid is discharged,the carrier unit B transporting the spent sulfuric acid, and the useroffice C utilizing the spent sulfuric acid, alternatively, at two ormore of the discharge source, the carrier unit, and the user office. Ajudgment index for judging whether or not concentration adjustment isneeded is obtained by performing the concentration measurement in thisway. When concentration adjustment is performed, an index fordetermining a mixing weight ratio when the sulfuric acid waste liquid ismixed with hydrogen peroxide solution and/or water is obtained.

The invention aims at enhancing the added value of the sulfuric aidwaste liquid by mixing the spent sulfuric acid waste liquid with atleast one of hydrogen peroxide solution and water. There is noparticular limit to the order of mixing sulfuric acid waste liquid withhydrogen peroxide solution and/or water, and to a method of adjustingthe concentration of spent sulfuric acid waste liquid to a predeterminedvalue. Methods of adjusting the concentration of spent sulfuric acidwaste liquid to a predetermined value are a method of adding a constantamount (per volume or per weight) of hydrogen peroxide solution and/orwater to spent sulfuric acid waste liquid, and a method of adding apredetermined amount (per volume or weight) of hydrogen peroxidesolution and/or water to spent sulfuric acid waste liquid according to aresult of the measurement of the concentration. From the viewpoint ofquality control, the latter method is more preferable. Further,regarding the order of mixing, from the viewpoint of safety, it is morepreferable to add sulfuric acid waste liquid to hydrogen peroxidesolution or water. Incidentally, in the case where according to a resultof the measurement of the concentration, there is the necessity forincreasing the concentration of sulfuric acid waste liquid, sulfuricanhydride or fuming sulfuric acid may be added thereto. Further,preferably, the mixing weight ratio is determined so as to adjust theconcentration to a value needed at the user office. The hydrogenperoxide solution to be used for the concentration adjustment is notparticularly limited, as long as the hydrogen peroxide solution isoxidative. The quality grade of the hydrogen peroxide solution may beadjusted to that required at the user office. Thus, the quality grade ofthe hydrogen peroxide solution may be either a low level grade forindustrial use, or may be a high grade for reagent or electronicindustry use.

The above-mentioned concentration adjustment by the addition of hydrogenperoxide and/or water (if necessary, concentrated sulfuric acid,sulfuric anhydride or fuming sulfuric acid may be added) may beperformed at any one of the discharge source A, the carrier unit B, andthe user office C, alternatively, at two or more of the dischargesource, the carrier unit, and the user office.

The concentration measurement and the concentration adjustment may beperformed either at the same place or at different places. In the casethat the concentration measurement and the concentration adjustment areperformed at the same place, a result of the concentration measurementis directly sent to a concentration adjustment apparatus (sulfuric acidwaste liquid tank, concentration adjustment liquid, a concentrationadjustment liquid storing tank, an adjustment liquid supply pump, ablending tank, a concentration measuring apparatus provided in theblending tank and so forth) in the form of a signal. Thus, theconcentration can automatically be adjusted to a predetermined value. Onthe other hand, in the case that the concentration measurement and theconcentration adjustment are performed at different places, a result ofthe concentration adjustment can be transmitted to the next step byvarious means, such as orality, telephones, mails, and the Internet. Itis judged at a place, to which the result of the measurement istransmitted, according to the transmitted result whether spent sulfuricacid is used without change, or the concentration adjustment isperformed. When the concentration adjustment is performed, theconcentration adjustment liquid is added in such a way as to obtain adesired concentration, as above-mentioned. Incidentally, in theconcentration adjustment tank, the concentration measuring apparatus maybe installed so as to check whether the concentration of the spentsulfuric acid reaches a predetermined value after the concentrationadjustment liquid is added thereto.

The above-mentioned concentration adjustment by the addition of hydrogenperoxide and/or water (if necessary, concentrated sulfuric acid,sulfuric anhydride or fuming sulfuric acid may be added) to sulfuricacid waste liquid may be performed at any one of the discharge source A,the carrier unit B, and the user office C, alternatively, at two or moreof the discharge source, t a carrier unit, and the user office. However,preferably, the system has a concentration adjustment apparatus(sulfuric acid waste liquid tank, concentration adjustment liquid, aconcentration adjustment liquid storing tank, an adjustment liquidsupply pump, a blending tank, a concentration measuring apparatusprovided in the blending tank and so forth). The concentrationadjustment apparatus is not particularly limited. However, in the casewhere concentration adjustment apparatus is performed at the office A orC, preferably, the concentration adjustment apparatus is of theinstallation type. In the case where concentration adjustment apparatusis performed at the carrier unit B, preferably, the concentrationadjustment apparatus is a tank of a tank truck. The blending tank may beany tank, as long as this tank is enabled to tentatively store sulfuricacid waste liquid having undergone the concentration adjustment, and toshow corrosion-resistance against sulfuric acid and hydrogen peroxidesolution. Preferably, for instance, quartz glass is used as the materialof such a blending tank. Further, preferably, the blending tank has awaste liquid tank for temporarily storing spent sulfuric acid wasteliquid so as to supply spent sulfuric acid waste liquid, hydrogenperoxide solution, and water thereto, a concentration adjustment liquidstoring tank for storing concentration adjustment liquid, such ashydrogen peroxide solution and water, and a adjustment liquid supplypump for supplying such liquid thereto. Any material may be used as thematerial of each of the waste liquid tank, the concentration adjustmentliquid storing tank, and the adjustment liquid supply tank, as long asthe material shows corrosion-resistance against sulfuric acid andhydrogen peroxide solution, similarly as the material of the blendingtank. Further, a tank, such as a rotary pump and a diaphragm pump, whichare adapted to feed fluid due to a pressure difference, may be used asthe adjustment liquid supply pump.

According to the invention, an additional treatment other than themeasurement and/or the adjustment of the concentration of the spentsulfuric acid may be performed at least at one of the discharge sourceA, the carrier unit B, and the user office C. The additional treatment,which will be described in detail below, is, for example, a treatment ofconcentrating sulfuric acid contained in the spent sulfuric acid, atreatment of removing ingredients other than sulfuric acid, which arecontained in the spent sulfuric acid, or a treatment of adding anotheringredient other than the sulfuric acid, which is contained in the spentsulfuric acid, thereto.

The treatment of removing ingredients other than sulfuric acid containedin the spent sulfuric acid is cited as exemplifying the additionaltreatment. Specifically, spent sulfuric acid discharged in the technicalfield of metal plating frequently contains metal ions. Thus, a treatmentof eliminating such metal ions can be cited as exemplifying thetreatment of removing ingredients other than sulfuric acid. A treatmentof using anion-exchange membrane and separating metal ions from asolution, which contains acid and metal, by utilizing a concentrationdifference therebetween as a driving force to thereby that is, what iscalled diffusion dialysis is cited as exemplifying the treatment ofeliminating the metal ions (see Japanese Patent Application PublicationLaid-Open No. 08-000966). Many documents and patents concerning membranefor performing diffusion dialysis on acid are reported. Anion-exchangemembrane obtained by amination of (or introduction ofquaternary-pyridinium groups to) chlormethyl-styrene (or vinylpyridine)-divinylbenzene copolymer is most practical and useful.

Treatments of removing excessive hydrogen peroxide solution from spentsulfuric acid containing the hydrogen peroxide solution so as to obtaina predetermined concentration of a hydrogen peroxide solution are citedas exemplifying the treatment of removing ingredients other thansulfuric acid contained in the spent sulfuric acid. More specifically, atreatment of decomposing hydrogen peroxide by simultaneously supplyinghydrogen to a hydrogen peroxide decomposing catalyst (see JapanesePatent Application Publication Laid-Open No. 61-186208), and a treatmentof decomposing hydrogen peroxide by letting waste liquid, whosetemperature is raised, through a carbonaceous material (see JapanesePatent Application Publication Laid-Open No. 5-345188) are cited.Moreover, a treatment of introducing sulfurous acid into spent sulfuricacid, which contains hydrogen peroxide solution, and causing thehydrogen peroxide and the sulfurous acid to react with each otherthereby to decompose hydrogen peroxide and to produce sulfuric acid, andpreventing sulfurous acid by detecting the sulfurous acid fromexcessively being added thereto, and then eliminating residual sulfurousacid by aerating the spent sulfuric acid after the introduction of thesulfurous acid is stopped (see Japanese Patent Application PublicationLaid-Open No. 9-315806).

The added value of spent sulfuric acid, which has hitherto been noteffectively utilized, or which has been sold at low price, can bedramatically increased (as that of a valuable resource) by using theabove-mentioned method. There are three modes of selling spent sulfuricacid are a case that a result of measuring the concentration istransmitted to a purchaser without changing the spent sulfuric acid, acase that the spent sulfuric acid, to which concentration adjustmentliquid, such as hydrogen peroxide solution and/or water, is added(incidentally, the concentration thereof is indefinite after theconcentration adjustment liquid is added), is sold, and a case that thespent sulfuric acid, to which concentration adjustment liquid is added,is sold by adjusting the concentration thereof to a predetermined value(incidentally, the value of the concentration is checked). When thespent sulfuric acid is soled, volume (or capacity) or weight thereof maybe employed as a basis for sales. Alternatively, the spent sulfuric acidmay be sold according to a result of the concentration measurement byusing the content of pure sulfuric acid as the basis for sales. When thespent sulfuric acid is sold without change, that is, without performingthe concentration adjustment, the concentration of the spent sulfuricacid varies at the discharge source. Therefore, it is more rational (orquantitative) to sell the spent sulfuric acid on the basis of the puresulfuric acid content.

A system for recycling spent sulfuric acid according to the inventioncan repeat the treatment a plurality of times. That is, sulfuric acidrecycled by the system for recycling spent sulfuric acid according tothe invention may be provided thereto again. More specifically,circulation of the recycling, which is represented by the nextexpression: Discharge Source A→Carrier unit B→User Office C (=DischargeSource A′→Carrier unit B′→User Office C′)n (in the expression, “n”designates a natural number, preferably, a natural number ranging from 1to 7, and incidentally, in the case that “n” is equal to or larger than2, A′, B′, and C′, which correspond to a different value of “n”, may beeither the same as or differ from A, B, and C, respectively.

The system for recycling spent sulfuric acid according to the inventionmay have the following system mode. That is, the system cited herein hasa spent sulfuric acid information management unit connected to aterminal of the discharge source A, and a terminal of the user office C,through a network, for example, the Internet and a LAN. The systemcomprises (a) means for inputting information on spent sulfuric acid,(b) means for storing the information on the spent sulfuric acid, (c)means for inputting conditions concerning spent sulfuric acid to besupplied, (d) means for retrieving information, which meets at leastpart of the conditions inputted by means (c), from the informationstored in the means (b), and (e) means for transmitting the information,which is obtained as a result of retrieval performed by the means (d),to the terminal of the discharge source A, to which the information ispresented, and/or to the terminal of the user office, from whichretrieval conditions are inputted. Furthermore, the spent sulfuric acidmanagement unit is also connected to a terminal of the carrier unit Bthrough a network, and has (f) means for transmitting to the terminal ofthe selected carrier unit B information concerning transportation ofspent sulfuric acid waste liquid.

<Embodiments>

The invention is specifically described hereinbelow by the embodiments,however, the invention is not limited thereto.

For comparison, a flow of a conventional treatment of spent sulfuricacid is illustrated in FIGS. 1A, 1B, 2, and 3. For example, spentsulfuric acid discharged from a semiconductor office and a plant issometimes subjected to a wastewater treatment together with otheralkaline/acidic leaning liquid, as shown in FIG. 1A. Then, acidic oralkaline neutralizer and various wastewater treatment agents are appliedthereto. Thereafter, the spent sulfuric acid changed into wastewater andsludge. Further, as illustrated in FIG. 1B, sometimes, only wastesulfuric waste liquid is collected. The collected liquid is utilized asa neutralizer (or acid), and then subjected to a wastewater treatment.Furthermore, as illustrated in FIG. 2, spent sulfuric acid waste liquidis sometimes taken over to a specialized processor, and subjected torefinement and recovery. More specifically, after collected, spentsulfuric acid waste liquid is transported a long distance, and deliveredto a user. Then, the spent sulfuric acid waste liquid is subjected torefinement and recovery treatments in a large-scale plant. Thus, thespent sulfuric acid waste liquid is used as materials of waste sulfuricacid and alum. For example, as illustrated in FIG. 3( c), the spentsulfuric acid is sometimes subjected to a refinement treatment in alarge-scale plant, and subsequently, transported a long distance anddelivered to a user. As illustrated in FIG. 3( d), spent sulfuric acidis sometimes subjected to a mixing treatment in a large-scale plant.After recycled, the recycled sulfuric acid is transported a longdistance, and delivered to a user. Furthermore, as illustrated in FIG.3( e), spent sulfuric acid is sometimes discarded after subjected to awastewater treatment in a large-scale plant.

FIGS. 4A to 4C illustrate a mode of a system for recycling spentsulfuric acid according to the invention. In this mode, measurement ofthe concentration of spent sulfuric acid is performed at one of adischarge source A (in a case illustrated in FIG. 4A), a carrier unit B(in a case illustrated in FIG. 4B), and a user office C (in a caseillustrated in FIG. 4C). In the cases respectively illustrated in FIGS.4A and 4B, information representing a result of the measurement of theconcentration is transmitted to the user office C.

FIG. 5 illustrates another mode of the system for illustrating spentsulfuric acid according to the invention. In this embodiment, theconcentration of spent sulfuric acid is adjusted according to a resultof measurement of spent sulfuric acid. More specifically, as illustratedin (A) of FIG. 5, the measurement of the concentration of spent sulfuricacid is performed at the discharge source A. Then, adjustment of theconcentration of spent sulfuric acid is performed according to a resultof the measurement of the concentration. Subsequently, recycled sulfuricacid, whose concentration has been adjusted, is provided to a user C bya carrier unit B. In (C) of FIG. 5, there is shown a case thatconcentration measurement and concentration adjustment based thereon areperformed by the user C instead of the discharge source A. Further,measurement of the concentration of spent sulfuric acid is conducted atthe carrier unit B. A result of the measurement is transmitted to theuser C. The user C may perform the concentration adjustment according toa result of the measurement thereof transmitted thereto (see (B) of FIG.5).

A more specific mode of the system for recycling spent sulfuric acidaccording to the invention is illustrated in FIG. 6. In this mode, spentsulfuric acid, which is collected from a semiconductor plant andcontains a hydrogen peroxide solution, is recycled as a mixture solutionof sulfuric acid and hydrogen peroxide solution at a cathode-ray tubeplant. More specifically, at the semiconductor plant, spent sulfuricacid containing hydrogen peroxide solution (designated as sulfuric acidhydrogen peroxide solution wasted liquid in FIG. 6, and hereunderabbreviated as “sulfuric acid hydrogen peroxide solution waste liquid”)is collected and stored in a sulfuric acid hydrogen peroxide solutionwaste liquid tank. A tank truck is used as the carrier unit B. Thus, thesulfuric acid hydrogen peroxide solution waste liquid is transported tothe cathode-ray tube circuit board plant. At that time, an owner of thetank truck may purchase the sulfuric acid hydrogen peroxide solutionwaste liquid from the semiconductor plant and sells the sulfuric acidhydrogen peroxide solution waste liquid to the cathode-ray tube circuitboard plant in addition to transportation of the sulfuric acid hydrogenperoxide solution waste liquid. At the cathode-ray tube circuit boardplant, the concentration of the transported sulfuric acid waste liquidis measured. Then, hydrogen peroxide solution and water are addedthereto when needed. Thus, sulfuric acid containing hydrogen peroxidesolution at a predetermined mixing ratio is produced. Thereafter, thissulfuric acid is used for peeling photoresist film and used as peelingliquid for copper foils. Incidentally, a hydrogen peroxide solution usedfor concentration adjustment may be a used hydrogen peroxide solution.

Further, FIG. 6 illustrates a case where the system for recycling spentsulfuric acid according to the invention is successively and repeatedlyused twice. That is, sulfuric acid hydrogen peroxide waste liquiddischarged at the semiconductor plant is recycled at a chemical plantaccording to the recycling system according to the invention. Moreover,sulfuric acid hydrogen peroxide solution waste liquid discharged at thechemical plant is recycled at the cathode-ray tube circuit board plant.Incidentally, in FIG. 6, details of the steps are not illustrated.

FIG. 7 illustrates a more specific mode of a method for recycling spentsulfuric acid. In this mode, spent sulfuric acid, which is collectedfrom a semiconductor office or plant and contains hydrogen peroxidesolution, is recycled and utilized at the cathode-ray tube manufacturingoffice or plant as peeling liquid for photoresist film. Morespecifically, at the semiconductor plant, spent sulfuric acid containinghydrogen peroxide solution (designated as sulfuric acid hydrogenperoxide solution wasted liquid in FIG. 7, and hereunder abbreviated as“sulfuric acid hydrogen peroxide solution waste liquid”) is collectedand stored in a sulfuric acid hydrogen peroxide solution waste liquidtank. A tank truck is used as the carrier unit B. Thus, the sulfuricacid hydrogen peroxide solution waste liquid is transported to thecathode-ray tube circuit board plant. At that time, an owner of the tanktruck may purchase the sulfuric acid hydrogen peroxide solution wasteliquid from the semiconductor plant and sells the sulfuric acid hydrogenperoxide solution waste liquid to the cathode-ray tube circuit boardplant in addition to transportation of the sulfuric acid hydrogenperoxide solution waste liquid. At the cathode-ray tube circuit boardplant, the concentration of the transported sulfuric acid waste liquidis measured. Then, one more of hydrogen peroxide solution and/or wateris added thereto in such a way as to have a desired concentration. Thus,sulfuric acid containing a hydrogen peroxide solution at a predeterminedmixing ratio is produced in a blending tank. Thereafter, this sulfuricacid is used for peeling photoresist film and used as peeling liquid forcopper foils. Incidentally, a hydrogen peroxide solution used forconcentration adjustment may be a used hydrogen peroxide solution.

The quality grade of recycled sulfuric acid obtained in this mode isequivalent to that of peeling liquid (low-concentration sulfuric acidhydrogen peroxide solution mixture liquid) hitherto purchased forpeeling off photoresist film by the cathode-ray tube manufacturingoffice or plant from a medicine maker. This can contribute to effectiveutilization of spent sulfuric acid waste liquid by recycling thereof andto reduced manufacturing cost in the cathode-ray tube manufacturingoffice or plant.

FIGS. 8A to 8C illustrates another mode of the method for recyclingspent sulfuric acid according to the invention. In this mode, adjustmentof concentration of spent sulfuric acid by adding one or more ofhydrogen peroxide solution and/or water according thereto is performedaccording to a result of measurement of concentration of spent sulfuricacid waste liquid. More specifically, as illustrated in FIG. 8A, themeasurement of the concentration of spent sulfuric acid waste liquid isperformed at the discharge source A. Then, adjustment of concentrationof spent sulfuric acid by adding one or more of hydrogen peroxidesolution and/or water according thereto is performed according to aresult of the measurement. Subsequently, recycled sulfuric acid, whoseconcentration is adjusted, is provided to the user office C by using thecarrier unit B. FIG. 8C illustrates a case that concentrationmeasurement and concentration adjustment according thereto are performedby the user office C instead of the discharge source office A. Further,the following process may be performed. That is, measurement of theconcentration of spent sulfuric acid is performed at the carrier unit B.A result of the measurement is transmitted to the user office C. Theuser office C may perform concentration adjustment by adding one or moreof hydrogen peroxide solution and/or water according to a result of themeasurement of the concentration (see FIG. 8B).

INDUSTRIAL APPLICABILITY

According to the invention, an added value of spent sulfuric aciddischarged from a certain office is enhanced and effective utilizationof the spent sulfuric acid is promoted by adding at least one ofhydrogen peroxide and/or water to the spent sulfuric acid. Moreover,according to the invention, there is no particular necessity for a largeoffice so as to enhance the added value of spent sulfuric acid. Thus,recycling thereof is almost not affected by the location. Consequently,the recycling of spent sulfuric acid is promoted. Cut-down of awastewater treatment agent for treating spent sulfuric acid, andreduction of amounts of sludge and wastewater are enabled. Especially,in the case where a discharge source A and a user office C belong to thesame company, the same group of companies, or the same group ofaffiliated companies, advantages of the invention are dominantlyenhanced.

1. A method for recycling sulfuric acid waste liquid which containshydrogen peroxide, characterized in that spent sulfuric acid wasteliquid containing hydrogen peroxide discharged/collected at a dischargesource is utilized by being mixed with hydrogen peroxide solution andwater.
 2. The method for recycling sulfuric acid waste liquid accordingto claim 1, characterized in that a concentration of a metal ingredientcontained in the spent sulfuric acid waste liquid is equal to or lessthan 10 ppb, and that a concentration of chloride contained in the spentsulfuric acid waste liquid is equal to or less than 0.1 ppm.
 3. Themethod for recycling sulfuric acid waste liquid according to claim 1,characterized in that the spent sulfuric acid waste liquiddischarged/collected at the discharge source is utilized at a useroffice C other than the discharge source.
 4. The method for recyclingsulfuric acid waste liquid according to claim 1, characterized in thatthe concentration of the spent sulfuric acid is adjusted according to aresult of measuring thereof.
 5. The method for recycling sulfuric acidwaste liquid according to claim 1, characterized in that when the spentsulfuric acid discharged or collected at the discharge source istransported by a carrier unit and used at a user office, a concentrationof the spent sulfuric acid is measured and/or adjusted at least at oneof the discharge source, the carrier unit, and the user office torecycle only spent sulfuric acid having 50 to 98 Wt % in a concentrationof the sulfuric acid.
 6. Recycled sulfuric acid manufactured by using amethod for recycling sulfuric acid waste liquid, characterized in thatspent sulfuric acid waste liquid containing hydrogen peroxidedischarged/collected at a discharge source is utilized by being mixedwith hydrogen peroxide solution and water.
 7. The recycled sulfuric acidaccording to claim 2, characterized in that a concentration of a metalingredient contained in the spent sulfuric acid waste liquid is equal toor less than 10 ppb, and that a concentration of chloride contained inthe spent sulfuric acid waste liquid is equal to or less than 0.1 ppm.